The present invention relates to bidirectional force limiters and, more particularly, to a force limiter designed to limit the magnitude of a force applied in either direction along a line of action to a safe, predetermined level.
There are many mechanical devices which are actuated between first and second positions, such as operative and inoperative positions, by the application of an actuating force along a line of action. In many of these force actuation environments, there is a need to limit the magnitude of the applied force to a predetermined value for safety or operational reasons. An example of one such environment is the handling and transportation of standard-sized cargo-containers in which container handling structures, known as spreaders, are used for attaching to and detaching from the container to assist in moving the container from one location to another, such as from the deck of a container ship to a railroad flat car or highway truck. The spreaders, in one exemplary design, include a trusslike structural steel frame which is sized to straddle and fit over the container and a plurality of depending arms and lock assemblies which are adapted to engage and lock onto the container. The locks are generally of the twist type which are selectively actuatable by the application of a force, for example, from an hydraulic actuator, between an unlocked position and a locked position to either detach or attach the container and spreader. When the spreader is attached to the container, the spreader may be lifted, for example, by a gantry-like hoist or crane to transport the container. Spreaders of this type have found widespread use in the loading and unloading of container ships as well as in the transferring of containers to and between railway flat cars and highway trucks.
For safety reasons, it is important that force applied to the twist locks be limited to a predetermined magnitude to prevent excessive force from being applied to a temporarily jammed lock thereby causing damage to the lock and to prevent excessive force from overriding mechanical safety devices designed to prevent unlocking when the container and spreader are in a suspended position.
Consequently, it is a broad overall object of the present invention to provide a force limiter to limit a force applied along a line of action to a predetermined magnitude.
It is another object of the present invention to provide a force limiter for limiting the force applied in either direction along a line of action to a predetermined magnitude.
It is still another object of the present invention to provide a force limiter for limiting the magnitude of an applied force which includes a force bias means adapted to yield in response to the applied force.
It is a further object of the present invention to provide a force limiter for use in combination with a spreader for handling and transporting cargo containers in which the locking and unlocking force applied to locking assemblies mounted on the spreader are limited by the force limiter to a safe, predetermined magnitude.